In rocket engines, thrust is typically generated by hot combustion gas expanding in a nozzle of a thrust chamber, the gas being produced by an exothermic chemical reaction within the thrust chamber. Thus, in operation, high pressures exist in the thrust chamber. In order to be able to continue to feed the thrust chamber in spite of those high pressures, the propellants need to be injected at pressures that are higher still. For this purpose, various means are known in the state of the art.
One known solution consists in using turbopumps. A turbopump comprises at least one pump driven by a turbine. In engines using the so-called “expander” cycle, the turbine is actuated by one of the propellants after it has passed through a heat exchanger in which it is heated by the heat produced in the thrust chamber. Thus, this transfer of heat can contribute simultaneously to cooling the walls of the thrust chamber and to actuating the pump of the turbopump.
Nevertheless, the use of expander cycle engines is limited.
As from a certain level of thrust, the energy available for feeding the turbine is limited by the capacity for extracting heat flux via the heat exchanger. In order to overcome this limitation, it is necessary to increase the length and the weight of the thrust chamber.
Furthermore, in order to govern the mixing ratio of the propellants, which is done by acting on the flow rate(s) through the turbine, other members and arrangements are necessary.
Another solution consists in pressurizing the tanks containing the propellants. Nevertheless, that approach puts a limit on the maximum pressure that can be reached in the thrust chamber, and thus on the specific impulse of the rocket engine. Another drawback of that solution lies in the use of low-performance propellants that are dense in order to limit the weight of the pressurization fluids. Propellants of low density lead to using tanks of large volume that therefore require large weights of pressurizing gas, and that leads to an increase in the overall weight of the rocket engine.